Conventional electronic modules for control units, for example known electronic modules for transmission control units, are usually designed as hermetically sealed modules. Said modules have, for example, a metal housing through which contact pins are routed to the outside. In this case, the contact pins are sealed by glass sealing. Advanced electrical connection technology to form individual functional elements in the module, for example to form sensors, internal and external plugs, is usually realized with so-called stamped grids which can be partially encapsulated in plastic, or else, for example, is designed with cable connections in the case of remote functional elements.
A further design of electronic modules is shown according to FIG. 1a. In this case, the electronic module 1 is again designed in a hermetically sealed manner and has a covering element 4 and also a support element 7. A component support printed circuit board element 2, which is coupled to further printed circuit board elements 3 using contact-making elements 6, is interposed between covering element 4 and support element 7 in a region 24 inside the covering element 4. Said further printed circuit board elements, for their part, are arranged and designed in such a way as to provide a connection between the region 24 inside the covering element 4 and the region 26 outside the covering element 4.
According to FIG. 1a, the result is therefore a basic layer structure of a support element 7 and a printed circuit board element 3 which is mounted on said support element and is closed off by a covering element 4.
Support element 7 can be designed, by way of example, as a metal plate, for example an aluminum plate with a sheet thickness of from 3 to 4 mm. Component support printed circuit board element 2, by way of example in the form of a low temperature cofired ceramic (LTCC) or micro printed circuit board, is mounted on said support element, for example adhesively bonded using a thermally conductive adhesive 8.
Printed circuit board element 3, which is provided with a cutout 15, is likewise mounted on the support element 7, for example adhesively bonded over a wide area in an oil-tight manner using an adhesive 9, a liquid adhesive agent or an adhesive strip. In this case, printed circuit board element 3 realizes the electrical connection between the electronic components on component support printed circuit board element 2 and the external functional elements, such as plugs, sensors etc. of the electronic module 1 for example.
Covering element 4 is provided and fastened on the printed circuit board element 3 by a sealing adhesive connection 10 in order to protect the electrical components of the component support printed circuit board element 2 and the contact-making elements 6, for example bonds, against external influences such as transmission oil, metal chips and other conductive debris for example.
Owing to different degrees 12, 13, 14 of thermal expansion of printed circuit board element 3, covering element 4 and adhesive connection 10, the adhesive connection 10 is subjected to shearing stress, but this can lead to failure of the adhesive connection. As a result, it is possible for leaks to occur, in particular the hermetic sealing of the inside region 24 can fail.
An internal excess pressure 16 of, for example, 0.5 bar can be produced by temperature swings of, by way of example, −40° C. to +150° C. This can also subject the sealing adhesive connection 10, in particular, to tensile loading. If the covering element 4 deforms, even slightly, further owing to the increase in pressure, the adhesive connection 10 may additionally further be subject to peeling.
As shown in FIG. 1b, there is likewise a relatively large active pressure area 17 which additionally subjects the adhesive connection 9 between printed circuit board element 3 and support element 7 to loading by a force 18.